1. Field of the Invention
The invention relates to a semiconductor device and a method of manufacturing the same.
2. Description of the Related Art
A high-power mesa diode has been conventionally known as one of semiconductor devices. A conventional mesa diode will be described referring to FIG. 8.
An N− type semiconductor layer 111 is formed on the front surface of an N+ type semiconductor substrate 110. A P type semiconductor layer 112 is formed on the front surface of the N− type semiconductor layer 111, and an insulation film 113 is formed on the P type semiconductor layer 112. An anode electrode 114 electrically connected to the P type semiconductor layer 112 is further formed.
A mesa groove 117 is formed from the front surface of the P type semiconductor layer 112, reaching the N− type semiconductor layer 111. The mesa groove 117 is formed deeper than the N− type semiconductor layer 111, and the bottom thereof is located in the N+ type semiconductor substrate 110. The width W7 of the mesa groove 117 is 50 to 100 μm, for example, and the depth is about 100 μm, for example. An insulating material 118 is deposited in the mesa groove 117 so as to cover the sidewall thereof. This mesa groove 117 functions as a so-called guard ring. The mesa diode is surrounded by the mesa groove 117 and has a mesa structure. A cathode electrode (not shown) is formed on the back surface of the semiconductor substrate 110.
A mesa semiconductor device is described in Japanese Patent Application Publication No. 3985582.
However, in the mesa diode described above, when the insulating material 118 is deposited in the mesa groove 117, the insulating material 118 is deposited on and near the bottom of the mesa groove 117 more than needed, and on the other hand, it is formed thinner than desired on the sidewall of the mesa groove 117 in regions 117C at and near the PN junction portion of the N− type semiconductor layer 111 and the P type semiconductor layer 112. This causes a problem of reducing the breakdown voltage at the PN junction portion in the mesa groove 117 that functions as the guard ring.
To address this, it is conceived that the process of depositing the insulating material in the groove is repeated several times so as to provide the insulating material 118 with enough thickness at the end on the sidewall of the mesa groove 117 in the regions 117C at and near the PN junction portion.
However, this method causes complex processes and increases the processing time, and also makes it difficult to form the insulating material 118 stably with desired accuracy. Furthermore, it causes a problem of largely increasing the amount of the insulating material 118 deposited in the mesa groove 117 more than the amount usually needed. As a result, the manufacturing cost of the mesa diode is increased.